In many applications, transistor devices are used. For example, transistor devices may be used as switches in electronic power applications. Various transistor types have been employed as switches, for example bipolar transistors like bipolar junction transistors (BJTs) or insulated gate bipolar transistors (IGBTs), or unipolar transistors like metal oxide semiconductor field effect transistors (MOSFETs). Such transistors and corresponding transistor devices including one or more transistors and possibly additional circuitry are available in different designs to support various voltages and/or currents.
Many electronic power applications operate under partial load over most of the time, and require operation under a maximum load (for example maximum current or power) only part of the time. An example for such an application are switched mode power supplies (SMPS), in which typically during about 80% of the operation time only 20% or less of a maximum power is needed. Nevertheless, such devices have to be configured to tolerate a maximum possible power to prevent failures. Also for higher voltage ranges, for example voltages above 1700 V, many applications exist which switch between full load and partial load, for example converters for solar or wind power plants or application in power trains of vehicles, where for starting of an engine full load is required, whereas, during normal driving only a part of the full power is needed.
Different transistor types may have different drawbacks and advantages when employed in such applications. For example, IGBTs are advantageous for high currents, but under partial load often suffer from a comparatively low efficiency. On the other hand, some unipolar transistor switches like MOSFETs may have a lower efficiency under full load and/or may require large chip areas. In particular, in case of overcurrents, bipolar transistors, in particular IGBTs, have better capabilities than MOSFETs.
It is therefore an object to provide transistor devices with improved handling of overcurrents, while still providing good capabilities under partial load, for example low currents.